The present invention relates to an attaching method of a fuel rail assembly for a direct-injection engine.
Conventionally, a direct-injection engine which injects fuel directly through a fuel injector projecting into a combustion chamber of the engine is known in vehicles, such as automotive vehicles. In an inline type of direct-injection engine equipped with plural cylinders arranged in line, high-pressure fuel is supplied to respective fuel injectors for the plural cylinders via a fuel rail. This fuel rail comprises a rail member extending straightly along a cylinder-line direction to supply the fuel therethrough, plural cup portions to deliver the fuel from the rail member to the respective fuel injectors, and plural boss portions to fasten the fuel rail to a cylinder head thereby, which delivers the fuel from a fuel pump of the engine to the respective fuel injectors for the plural cylinders.
When the fuel injectors are attached to the engine, a fuel rail assembly in which the fuel injectors are attached to the fuel rail in advance is formed, and then this fuel rail assembly is fastened to the cylinder head with plural bolts corresponding to the respective cylinders. Each of the fuel injectors of the fuel rail assembly is inserted into the cup portion via a base-end-portion seal ring member arranged at a base-end portion of the fuel injector, that is, the fuel injector is arranged in a so-called one-sided support state. Therefore, there is a concern that a small-diameter cylindrical portion at a tip portion of the fuel injector may not be correctly positioned in its injector-insertion hole, so that the small-diameter cylindrical portion of the fuel injector may interfere with the cylinder head improperly. Therefore, a positioning adjustment of the fuel injector is generally conducted prior to pressing and inserting the small-diameter cylindrical portion of the fuel injector into the injector-insertion hole.
Japanese Patent Laid-Open Publication No. 2010-19132 discloses an attaching method of a fuel rail assembly, in which a fastening receiving seat is formed at a cylinder head, a bar-shaped guide member which is detachable relative to a screw hole formed at the fastening seat is provided, and a detachable stopper member is provided at a midway portion of the guide member which corresponds to where a tip of a small-diameter cylindrical portion of a fuel injector approaches an injector-insertion hole. Herein, after the above-described guide member inserted into a boss hole of the above-described boss portion of the fuel rail assembly is attached to the above-described screw hole of the fastening receiving seat, the fuel rail assembly is moved toward the cylinder head along the guide member. Then, when this move of the fuel rail assembly is restricted by the stopper member, the position of the fuel injector relative to the injector-insertion hole is adjusted and the stopper member is detached, the small-diameter cylindrical portion of the injector is pressed and inserted into the injector-insertion hole, then bolts are fastened to the boss portion.
The attaching method of a fuel rail assembly disclosed in the above-described patent document has a concern that even if the fuel injector is adjusted at a proper position in the stage of moving toward the cylinder head, the fuel rail assembly may not be effectively fastened relative to the cylinder head due to its structure when the small-diameter cylindrical portion of the fuel injector is pressed and inserted into the injector-insertion hole.
First, it may be difficult to press the fuel rail and the plural fuel injectors together against the cylinder head by fastening the plural boss portions provided at the fuel rail with the bolts. Secondly, it may be difficult to align the axial center of the fuel injector with the axial center of the injector-insertion hole. That is, a processing error of the cup portions and a processing error of the injector-insertion holes may be accumulated complexly, so that an improper difference in position between the axial center of the fuel injector inserted into the cup portion and the axial center of the injector-insertion hole may occur.
The above-described first problem may be solved by providing spring members to provide a biasing force to overcome a combustion-pressure reaction force between the plural cup portions of the fuel rail and the plural fuel injectors, whereby proper attaching of the fuel injectors can be conducted by the biasing force of the spring members. Further, the above-described second problem may be solved by proving a holding ring which comprises a taper face and a ring-shaped contact portion having a line contact with the taper face between the fuel injector and the head-side seating portion, whereby the difference in position between the axial center of the fuel injector and the axial center of the injector-insertion hole can be properly absorbed (adjusted). In a case in which the axial center of the fuel injector slants relative to the axial center of the injector-insertion hole, the holding ring can adjust the contact position of the taper face with the ring-shaped contact portion with a reaction force of the base-end-portion seal ring member occurring in a perpendicular direction to the axial center of the fuel injector. That is, the fuel injector can be stably seated in a face of the head-side seating portion via the holding ring in spite of the axial center of the fuel injector slanting relative to the axial center of the injector-insertion hole.
In the attaching method of the above-described fuel rail assembly, the fuel rail assembly is formed by inserting the fuel injectors equipped with the holding rings into the cup portions of the fuel rail via the spring members, this fuel rail assembly is pressed toward the cylinder head and the fuel injectors are pressed and inserted into the injector-insertion holes, and then the plural boss portions of the rail member are fastened and fixed to the respective fastening receiving seats. In an actual manufacturing process, from a work-efficiency perspective, the plural fuel injectors are pressed and inserted concurrently, and then the fuel rail assembly is fastened to the fastening receiving seats of the cylinder head with plural bolts for the respective cylinders by using a multiple nut runner capable of concurrently fastening.
The above-described press inserting step can be easily achieved by pressing the rail member with a specified pressing apparatus. However, since the axial center of the fuel injector is restricted by the injector-insertion hole via the base-end-portion seal ring member, the difference in position between the fuel injector and the injector-insertion hole may cause a slant of the axial center of the fuel injector relative to the axial center of the injector-insertion hole. Thus, if the press and insertion direction of the rail member slants in a longitudinal direction of the rail member, there occurs some difference in a compressive reaction force between the respective spring members. Accordingly, if a frictional force between the holding ring and the head-side seating portion exceeds the reaction force of the base-end-portion seal ring member occurring in the perpendicular direction to the axial center of the fuel injector, the move (displacement) of the holding ring in the perpendicular direction to the axial center of the fuel injector becomes not adjustable, so that the position of the axial center of the fuel injector is restricted. In a case in which the axial-center position of a specified fuel injector is restricted with its slating toward a certain direction in the press inserting step, if the fuel rail is compulsorily moved toward the cylinder head prior to completion of this step, the difference (error) in the axial center between the fuel injector and the cup portion increases. Thus, there is a concern that the axial-center difference (error) of the above-described specified fuel injector may deteriorate extremely more than that of the other fuel injector. Additionally, in a case in which the timings of fastening bolts improperly vary in a fastening step after the press inserting step, there is a concern that the difference (error) in the axial center between the fuel injector and the cup portion may further increase.
Herein, while it may be considered that a pressing force of the rail member is cancelled once in a previous step prior to the fastening step, this cancelation merely causes a temporary releasing of the biasing force of the spring member, so that there is a concern that the axial-center difference (error) of the fuel injector may occur again when the re-press inserting step or the fastening step restart. Therefore, when the positional difference between the fuel injector and the cup portion is improperly large, there exists a portion where a face pressure in a peripheral face between the base-end-portion seal ring member and the cup portion decreases, in particular, the hardness of the base-end-portion seal ring member increases in a cold engine-operational state. Thus, there is a concern that the fuel seal may deteriorate at the portion with the decreased face pressure.